1. Field of Invention
The present invention relates to a technique for estimating the vehicle speed with high accuracy. More specifically, the present invention relates to a technique for estimating the vehicle speed with high accuracy to prevent the execution of an erroneous control by a vehicle control device such as, for example, an anti-skid control device (ABS), traction control device (TRC) or rear wheel steering device (4WS).
2. Description of Related Art
Generally, to properly execute a vehicle control operation that depends on the vehicle speed, the validity of wheel speeds, which are used as the basis for calculating the vehicle speed, is critical. In particular, if the vehicle is moving at a low speed, the validity of detection values may be dubious because the outputs from wheel speed sensors are below the detectable speed level. Thus, it is necessary to determine the validity of the wheel speeds accurately using the lowest calculated wheel speed value in other words, a valid wheel speed threshold.
For example, Japanese Patent Application Publication No. 7-257352 (JP-A-7-257352) describes a vehicle control device that selects the higher of the lowest calculated wheel speed value and a permission speed as a reference to permit vehicle control and compares the selected value and the vehicle speed to determine whether to execute the control operation.
However, the vehicle control device described in JP-A-7-257352 may not be able to perform a control operation properly depending on the lowest calculated wheel speed value when a constant speed traveling is performed at a low speed of 0 to 5 km/h as shown in Japanese Patent Application Publication No. 2004-90679 (JP-A-2004-90679). Also, the actual vehicle speed may deviate greatly from the target vehicle speed when a constant speed traveling is performed at a low speed.